A common semiconductor device is a dynamic random access memory (“DRAM”) device. The DRAM device is typically used for storing data, for example, in a computer system. Current DRAM devices are designed to operate synchronously in accordance with a system clock, which can have clock frequencies greater than 600 MHz. These devices are referred to as synchronous DRAM (“SDRAM”) devices. SDRAM devices can be used in a variety of applications, many of which are in compact environments with adjacent electronics devices in relatively close proximity to the SDRAM devices. A common example of such an environment is a conventional portable laptop computer, where SDRAM devices are enclosed in a small environment with other common computer devices and circuits, such as a microprocessor, a hard-disk drive, power circuits and battery, computer-controller chipsets, CD-ROM/DVD drive, wireless communication devices, and the like.
The computer devices and circuits must be designed to operate over a range of temperatures. During times where many of the devices and circuits are operated simultaneously, or operated for a long period of time, more heat is generated than when the computer is idle, or only a few of the devices or circuits are operating. As one can imagine, in such a small and cramped environment, the temperature in which the different devices and circuits operate can be considerable as a result of the heat that is generated as these devices and circuits operate and consume power. Under some higher temperature conditions, the performance of the various computer devices and circuits begin to degrade. For example, with respect to SDRAM devices, the hold time that data can be stored without the need to rewrite, or “refresh” the data, decreases as the operating temperature increases. In severe operating conditions, the temperature may be sufficient to cause some cells, which have acceptable hold characteristics under lower temperature conditions, to fail. Additionally, transistors included in the circuitry of the SDRAM devices may not be capable of providing the same drive current or switch at the same speed under higher temperature conditions, causing SDRAM device performance to degrade.
Various cooling methods are utilized to manage the temperature in which the computer devices and circuits operate. Some more common cooling methods utilized are providing a sufficient number of vents in a computer case to allow heat to escape, including electric fans which are activated when certain temperature conditions are met to create a cooling air flow for the devices and circuits, and thermal shut-down circuitry that will automatically shut-down, or discontinue operation of the computer to prevent irreparable damage to the computer devices and circuits from occurring. Another approach has been the use of devices and circuits that operate at lower voltages, or that are more energy efficient, to reduce power consumption. An obvious benefit is increasing the time battery-operated computers can be used. However, another benefit from reducing power consumption is reducing the amount of electrical energy that is transformed into heat energy during operation of the devices and circuits. Generating less heat generally results in lower operating temperatures.
A more recent proposal, with specific application for memory devices, such as SDRAM devices, is to design memory devices that include an integrated temperature sensor that is used to measure the temperature of the memory device. The memory device can be commanded to output data representative of the operating temperature condition as measured by the integrated temperature sensor. Based on the output data of the memory device, measures can be taken to maintain operability of the memory device, including actions to maintain or reduce the operating temperature of the memory device, or change operating conditions, such as increase refresh rate of the memory device. For example, if a memory controller receives data from a memory device having a temperature sensor indicating that a critical temperature has been exceeded, the memory controller can force the memory device into an idle state until the temperature is reduced to a sufficient level to resume operation.
Various protocols have been suggested as to the format of the data output by a memory device having a temperature sensor. One example is providing data having only a binary state, with one state indicating that the measured temperature of the memory device is below a temperature threshold value and the other state indicating that the measured temperature is above the temperature threshold. Although the output data of the memory device can be easily interpreted to provide an indication of the measured temperature relative of a single temperature threshold, this approach may be unacceptable where data representing greater temperature resolution is desired.
Another approach provides data having only a binary state indicative of measured temperature relative to a plurality of programmable temperature thresholds. In this approach, greater temperature resolution can be provided by the two-state data in comparison to the single temperature threshold approach by programming at least two temperature thresholds, one temperature threshold representing the upper boundary of a temperature range and another temperature threshold representing the lower boundary of the temperature range. In interpreting the output data of the memory device, one state of the data represents the condition that the measured temperature is within the programmed temperature range and the other state of the data represents the condition that the measure temperature is outside of the programmed temperature range. Alternatively, one of the states of the data can represent that the measured temperature has not crossed any of the temperature thresholds and a signal pulse of the other state represents the times at which the measured temperature crosses one of the programmed temperature thresholds. Although the data under this approach provides easily interpreted data having greater temperature resolution than the single temperature threshold approach, the state of the output data does not directly indicate if the measured temperature is greater than or less than the programmed temperature range, but simply whether the measured temperature is within the programmed temperature range. Thus, where even greater temperature resolution is desired, the previously described approach will be unacceptable. Additionally, programming the temperature thresholds adds complexity to the set-up and operation of memory devices having this feature.
One other approach to providing temperature data from an integrated temperature sensor is to output a data word that represents the temperature measured by the temperature sensor. The data word is sequentially output from several data input/output concurrently to provide redundancy confirmation, and timed with respect to a temperature command provided to the memory device in order for the correct bits of the data word to be latched. Although the temperature resolution provided by this approach is greater than the previously described approaches, the timing of sequentially outputting the bits of the data word and latching the same is much more critical for accurately interpreting the temperature data. If either the output or latching of the sequence of bits of the data word is not timed correctly, for example, beginning a clock cycle early or late, the wrong bits will be interpreted as the temperature value. Additionally, sequentially outputting the data word can interfere with normal read and write operations that occur immediately following the output of the temperature data.
Therefore, there is a need for a system and method of providing temperature information from an integrated temperature sensor that provides adequate temperature resolution and ease in interpreting the temperature data.